Alison, Norfolk asked:
If a mosquito bites someone with HIV and then goes and bites someone else will it pass on the disease?
Chris - Thankfully, no. Because otherwise Africa would have a much worse problem than it currently has where there are something like 4 million new cases of HIV every year. Theyíre thankfully not caused by mosquitoes. If they were we would all be in really serious trouble because it would be like malaria. The reason is really simple because we know that mosquitoes are very good at transmitting viruses, certainly things like dengue gets spread by mosquitoes and thatís a virus.
Thereís a very good reason why this isnít the case with HIV which is that HIV is a very specialist virus which has on its surface viral velcro, molecular docking stations that lock on to certain parts of cells, CD4+ cells which you only find in us, in humans. Thereís related versions of HIV in chimpanzees (SIV) and they have their own specific cells that it locks onto. Because those specialist cells are only found in us HIV is a very fragile virus. It canít survive in the mosquitoís intestine, it canít latch onto cells in the mosquito, therefore the mosquito doesnít get infected. Therefore the mosquito canít amplify the dose from the person it bites. Therefore it canít infect the next person because it canít inject more viruses than it took in. HIV is very poor at infectivity. Itís actually very hard to catch, believe it or not. You can reassure everyone youíre not going to catch HIV from a bite.